Nature of S-N Bonding in Sulfonamides and Related Compounds: Insights into π-Bonding Contributions from Sulfur K-Edge X-ray Absorption Spectroscopy.

Molecules containing sulfur-nitrogen bonds, like sulfonamides, have long been of interest because of their many uses and interesting chemical properties. Understanding the factors that cause sulfonamide reactivity is important, yet there continues to be controversy regarding the relevance of S-N π bonding in describing these species. In this paper, we use sulfur K-edge X-ray absorption spectroscopy (XAS) in conjunction with density functional theory (DFT) to investigate the role of S3p contributions to π-bonding in sulfonamides, sulfinamides, and sulfenamides. We explore the nature of the electron distribution of the sulfur atom to its nearest neighbors and widen our scope to its effects on rotational barriers along the sulfur-nitrogen axis. The experimental XAS data together with time-dependent DFT calculations confirm that sulfonamides-and the other sulfinated amides in this series-have essentially no S-N π bonding involving S3p contributions and that electron repulsion is the dominant force affecting rotational barriers along the S-N axis.